Bitumen recovery process

ABSTRACT

1 . A bitumen recovery process where the process includes the following steps:
         a) Drilling a single well into a bitumen deposit;   b) Equipping the well with a heating element, a solvent injecting member, and a bitumen recovering member;   c) Injecting the well with a solvent;   d) Heating the solvent with the heating element to a vapor state;   e) Mixing the solvent vapour with bitumen in the deposit;   f) Draining the bitumen to the bottom of the well;   g) Heating the bitumen to keep its viscosity low;   h) Evaporating part of solvent entrapped in the bitumen by the heating element;   i) Recovering the bitumen and traces of water from the well;   j) Condensing the solvent inside the well for further mixing with the bitumen in the deposit;   k) Repeating steps h through j, where the majority of the solvent does not leave the well during the process.

BACKGROUND OF THE INVENTION

There are several known techniques for enhanced oil recovery fromunderground formations. Some of those techniques use heating of theformation in order to increase the flow of bitumen and allow easierrecovery. One of these techniques is known as steam assisted gravitydrainage (SAGD).

Other enhanced oil recovery technologies include introducing a heatingelement to the underground formation. The heating element can be anytype known in the art, including the following: 1) a continuous tubehaving an electric heating element or 2) a continuous tube permittingcirculation of a heated fluid such as steam, gas, superheated liquid,molten salts, or other heated fluids known in the art. These heatingelements are typically utilized to preheat the underground formationprior to injection of the steam into the formation.

Further enhanced oil recovery technologies utilize a solvent assistedtechnique. The solvent assisted technique includes the followingsteps: 1) the solvent is injected into the formation; 2) the solvent ismixed with the bitumen; 3) the solvent/bitumen mixture is recovered fromthe bitumen formation; and 4) the solvent is separated from the bitumen,recycled and then used in the formation again.

Recent developments in enhanced oil recovery technologies include US2011/0303423. US 2011/0303423 teaches recovering in situ viscous oilfrom an underground reservoir. Electricity is conducted through theunderground reservoir by at least two electrodes in an amount thatwould, in the absence of solvent injection, cause water in the reservoirto vaporize adjacent to the electrodes. Solvent is injected into thereservoir to mitigate water vaporization adjacent to the electrodes byvaporizing solvent in this region. Oil and solvent are produced throughone or more production wells. However, the method disclosed in US2011/0303423 does not contemplate an energy efficient process thatreduces both solvent usage and water treatment procedures.

The known enhanced oil recovery technologies are heavily investigated,but still require improvements at every stage. The required improvementsinclude 1) simplifying oil recovery the process; 2) reducing the needfor materials such as steam and solvents thereby reducing energyconsumption for steam generation; 3) reducing water treatmentprocedures; and 4) improving the process solvent recovery from thebitumen mixture.

SUMMARY OF THE INVENTION

Disclosed herein is a process for recovering hydrocarbons such asbitumen from an underground formation which is designed to increaseenergy efficiency by reducing I) surface water treatment and 2) solventusage.

In one aspect, the bitumen recovery process comprises the followingsteps:

-   -   a) Drilling a single well into a bitumen deposit;    -   b) Equipping said well with a heating element, a solvent        injecting member, and a bitumen recovering member;    -   c) Injecting said well with a solvent having a low flash point        through said solvent injecting member;    -   d) Heating said solvent with the said heating element to a vapor        state while keeping the temperature and pressure in the well at        a predetermined condition;    -   e) Mixing said solvent vapor with bitumen in the deposit thus        reducing said bitumen viscosity;    -   f) Draining said bitumen to the bottom of the well proximate the        heating element;    -   g) Heating the bitumen to keep its viscosity low, enabling        recovery of the bitumen by bitumen recovering member;    -   h) Evaporating at least part of solvent entrapped in the bitumen        at the bottom of the well by the heating element;    -   i) Recovering said bitumen and traces of water from the well by        said bitumen recovering member;    -   j) Condensing said solvent inside the well for further reaction        with the bitumen in the deposit;    -   k) Repeating steps h through j, wherein the majority of said        solvent does not leave the well during the bitumen recovery        process.

In one embodiment, the heating element utilizes electricity, steam, or ahot fluid circulating through the well. In a further embodiment, theheating element utilizes electricity, steam, or a hot fluid circulatingthrough the well in a tube. In yet another embodiment, the electricity,steam, or hot fluid is reheated at the surface or in the bore of thewell.

In one embodiment, the solvent used in the process comprises propane,butane (normal, iso & mixed), pentane (normal, iso & mixed), or hexane(normal, iso & mixed). In a further embodiment, the solvent is a mixedsolvent with a composition from C3 to C8. In yet another embodiment, thesolvent is a mixed solvent with a composition from C5 to C7. Evenfurther, the solvent composition is a heavier C7 in the initial recoveryprocess and is progressively replaced with lighter hydrocarbons as theprocess continues In one embodiment, steam is injected into the wellalong with the solvent.

In one embodiment, the produced fluids recovered from the well areprimarily bitumen or heavy oil with a small amount of miscible containedsolvent and some connate water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of single well heating.

FIG. 2 is a cross-sectional view of the end of pre-heating the singlewell.

FIG. 3 is an alternative view of the end of pre-heating the single well.

FIG. 4 is a cross-sectional view of the single well near abandonment.

FIG. 5 is a production profile of single well heating.

FIG. 6 is a graph showing the production profile of single well heating.

FIG. 7 is a cross-sectional view of solvent recovery in single wellheating.

DETAILED DESCRIPTION

A well is drilled into the target formation. The entire operation may beachieved in a vertical well, slant well, horizontal well or an irregularwell having a combination of vertical, horizontal and tilted portions toadapt to the geometry of the formation. Even further, the horizontalwell can be extended from the vertical well.

A single well is used to achieve a gravity driven bitumen or heavy oilproduction process. However, multiple wells may be heated and producedsimultaneously or sequentially, each with their own heat string. Thewell is cased to the bottom of an intermediate casing, where thehorizontal section includes a thermal casing and thermal cement. In thehorizontal section, the well has a liner with either slotting or screensto control any sand influx.

As shown in FIG. 1, a string of tubing 2 is placed into the hole downthrough the vertical section and out into the horizontal section to adesired length. Then, the tube 2 subsequently curls back to return alongthe horizontal run and back to the surface 4. The tubing can be fullyinsulated, partially insulated, or non-insulated.

The tubing contains a heating medium 6 which could be electricity,steam, or another fluid with high-heat transfer characteristics. At thesurface 4, the electricity, steam, or fluid is reheated to the targettemperature and then returned to the portion of tubing string 2 in thewell. The electricity, steam, or fluid is at super-heated or saturatedsteam condition as it enters the well bore so that it transfers heat tothe horizontal section. This initial preheating of the formation createsand initiates a depletion chamber. Condensing may take place and,because of the phase change and fixed volume, a thermo-siphon effectwill be created.

After the preheating step, a solvent is introduced into the well.Preferably, in the horizontal section of the well, the solvent is addedthrough an additional tubing string. Preferably, the solvent is astraight chain hydrocarbon which is easily vaporized at the welltemperature and is miscible with the reservoir bitumen/oil. Morepreferably, the solvent is a light hydrocarbon such as butane,iso-butane, pentane, hexane or a mixed solvent with similar commercialdiluents with a composition from C3 to C8, but the bulk of the solventvolume in the C5-C7 range. Experiments have shown that xylene andnatural citric acid may also be used as solvents. Varying the solventcomposition over time may be helpful from heavier C7 to lighter C3 overthe production cycle. It should be kept in mind that the solventcomposition must be matched to the specific reservoir operatingconditions, ensuring a good vaporization and condensation temperaturethat matches the down hole temperature.

As shown in FIGS. 2 and 3, an initial fill of solvent in the horizontalwell bore should be sufficient to maintain the process. When the liquidsolvent reaches the tube heated by steam, the heat of condensation isreleased to the solvent. The solvent quickly heats to its boiling pointand vaporizes. Since vapor is lighter and has a lower density than theliquid phase, solvent vapor will rise in the well bore filling thedepletion chamber. The vapor will rise until it reaches a surface thatis cool enough to condense it. Generally, the cooling surface will bethe bitumen above the cased well. Once the vapor is condensed onto orwith the bitumen, a hydrocarbon mixture is created and the viscosity anddensity of the mixture are much lower than bitumen alone but higher thanpure solvent. The hydrocarbon mixture will flow by gravity down to thehorizontal section of the well, creating a void space above in thereservoir. The lighter hydrocarbon mixture falls into the horizontalsection of the well bore and meets with the heat of the steam tubingagain. This causes the solvent portion of the mixture to evaporate andrise into the void space in a new cycle. At the same time, the bitumenin the well bore is maintained at a warm temperature, which keeps itmobile.

As shown in FIG. 4, the mobile bitumen can be recovered from thehorizontal well by means known in the art. For example, a gas lift orelectric submersible pump system 12 can be used to lift the hot bitumento surface. Preferably, the heat source is positioned at ground level.However, it may be also positioned down hole, as when using a standardESP (electric submersible pump) which generates a significant amount ofheat in the pumping action. Furthermore, an electric heating source canbe used alone or in combination with other heating sources.

Based on the reservoir characteristics, if the proper solventcomposition and operating conditions are used, the solvent will stay inthe reservoir throughout the process without the need to top up thesolvent. This results in little or no solvent in the production fluidbecause the solvent remains a working fluid within the reservoir. Thesolvent has a repeating cycle consisting of being warm liquid in thehorizontal section to hot vapor rising through the reservoir to abitumen/solvent mixture flow back to the horizontal section. Because thesolvent remains a working fluid in the reservoir, there is no solventrecovery until the end of the process resulting in less solvent used inthe overall process.

Because there is minimal solvent injection in the process, energy isconserved because solvent recovery at the surface isn't typicallyneeded. Even if the bitumen recovered contains trace or small amounts ofsolvent, the solvent remaining in the bitumen results in a slightlyreduced viscosity and density, lowering any requirement for diluentadditions prior to sales or pipelining.

As depicted in FIGS. 5 and 6, the bitumen produced from this processwill still contain some water, since there is connate water entrappedaround the sand grains in the reservoir along with the bitumen. However,the volume of water in the well will be substantially lower. In fact,the 300% volume of water in the bitumen volume experienced in typicalSAGD operation is reduced to 15-30% volume of water in the bitumenvolume.

Shown in FIG. 7, upon depletion of the bitumen formation, the solventremaining inside the formation can be cooled, drained to the bottom ofthe well, and recovered from the well for future reuse.

As is seen from above, important advantages of this process include thefollowing:

-   -   1) Production costs will be significantly lower than traditional        CSS or SAGD processes. Because there is no added water, the        water doesn't have be lifted to surface, cleaned, and reused or        disposed. Likewise, there is no need to vapourize water for the        steam injection into the reservoir.    -   2) The environmental impact of the operation will be much lower        than traditional CSS or SAGD since there is no heavy water        usage.    -   3) Using and cycling a contained heated fluid can maintain the        well bore at very low pressures. This feature allows recovery of        deposits which are very close to the surface and too complicated        or even dangerous (in terms of potential steam release to the        surface) for SAGD or CSS processes. The amount of resources        suitable for this specific technology is huge in the Athabasca        region alone, and is almost unexplored internationally.    -   4) The process described above can be equipped with additional        machinery and equipment used in the enhanced oil recovery such        as an oil treating facility, water treating facility, heaters,        oil storage, power generating and pumping equipment known in the        art.

As many changes therefore may be made to the preferred embodiment of theinvention without departing from the scope thereof. It is consideredthat all matter contained herein be considered illustrative of theinvention and not in a limiting sense.

1. A bitumen recovery process comprising the following steps: a)Drilling a single well into a bitumen deposit; b) Equipping said wellwith a heating element, a solvent injecting member, and a bitumenrecovering member; c) Injecting said well with a solvent having a lowflash point through said solvent injecting member; d) Heating saidsolvent with the said heating element to a vapor state while keeping thetemperature and pressure in the well at a predetermined condition; e)Mixing said solvent vapour with bitumen in the deposit thus reducingsaid bitumen viscosity; f) Draining said bitumen to the bottom of thewell proximate the heating element; g) Heating the bitumen to keep itsviscosity low, enabling recovery of the bitumen by bitumen recoveringmember; h) Evaporating at least part of solvent entrapped in the bitumenat the bottom of the well by the heating element; i) Recovering saidbitumen and traces of water from the well by said bitumen recoveringmember; j) Condensing said solvent inside the well for further mixingwith the bitumen in the deposit; k) Repeating steps h through j, whereinthe majority of said solvent does not leave the well during the bitumenrecovery process.
 2. The process of claim 1 wherein the heating elementutilizes electricity, steam, or a hot fluid circulating through thewell.
 3. The process of claim 2 where said electricity, steam, or hotfluid circulate through the well in a tube.
 4. The process of claim 3where the tube is insulated or partially insulated.
 5. The process ofclaim 2 where the electricity, steam, or hot fluid are reheated at thesurface.
 6. The process of claim 2 where the electricity, steam, or hotfluid are reheated in the bore of the well.
 7. The process of claim 1wherein the solvent is pure light hydrocarbon solvent.
 8. The process ofclaim 6 where the pure hydrocarbon solvent comprises propane, butane(normal, iso & mixed), pentane (normal, iso & mixed), or hexane (normal,iso & mixed).
 9. The process of claim 1 wherein the solvent is a mixedsolvent with composition from C3 to C8.
 10. The process of claim 1wherein the solvent is a mixed solvent with composition from C5 to C7.11. The method of claims 8 and 9 where the solvent composition is aheavier C7 in the initial recovery process and is progressively replacedwith lighter hydrocarbons as the process continues.
 12. The process ofclaim 1 wherein there is steam injected into the well along with thesolvent.
 13. The process of claim 1 wherein the produced fluidsrecovered from the well are primarily bitumen or heavy oil with a smallamount of miscible contained solvent and some connate water.
 14. Themethod of claim 9 where the solvent composition is a heavier C7 in theinitial recovery process and is progressively replaced with lighterhydrocarbons as the process continues.